I have been using the Kenji Lopez method for years. Honestly, the best way to cook burgers at home unless you have the ability to grind your own meat and can cook it to a lower temperature to something like medium rare. Personally I wouldn't eat a burger eating commercial beef unless you cook to 160. With smash method you don't need to worry about that aspect as it just comes out awesome.
Not sure if others follow his stuff on Serious Eats but he has some great stuff.
Use your grill and put your cast iron on it, I have a nice cast iron grill pan I got from Costco specifically for this. It's completely flat, will be doing smash burgers this weekend I think.